Process for making bright yarns

ABSTRACT

A process is disclosed for making thermostable bright yarns by the wet-spinning of a solution in a polar organic solvent of a copolymer containing both amide-imide groups and amide-acid groups with a content of free COOH groups at least equal to 0.5 milliequivalent of acid per gram of copolymer, having an inherent viscosity of between 0.7 and 1.4 and obtained by reacting, at a temperature below 80*C solution of polyamideimide in a polar organic solvent, and a polyamide-acid prepolymer in solution in the same polar solvent, in proportions of 15 to 50, referred to the copolymer.

Foreign Application Priority Data Aug. 12, 1971 France 71.29799 [52] US. Cl. 260/78 TF; 264/184; 264/210 F [51] Int. Cl. C08G 20/00; DOlD 5/06 [58] Field of Search 260/47 CB, 78 TF, 857 P1;

[56] References Cited UNITED STATES PATENTS 3.489.696 1/1970 M11161 260 857 Pl 3,528,937 9 1970 Reynolds Ct al 264/178 F 3,582,458 6/1971 Hallel 260/857 PI 3,673,160 6 1972 Buisson et a1 264/184 United States Patent 1 91 1111 3,903,058

Allard et a1. Sept. 2, 1975 [54] PROCESS FOR MAKING BRIGHT YARNS 3,708,459 l/1973 Lubowitz 260/78 TF 3,717,696 2/1973 Rochina et a]. 264/205 [75] lnvemos- Allard 3,733,308 5/1973 Bach 260 78 TF Calloux-Sur-Fontames; Francois Buisson, Colman both f France FOREIGN PATENTS OR APPLICATIONS Assigneez Rh0ne Poulenc Textile, Paris, 1,566,393 2/ 1967 France 264/ 184 France Przmary Exammer-.lay H. W00 [22] Filed: -Aug. 2, 1972 Attorney, Agent, or Firm-Stevens, Davis, Miller &

Mosher 5 7 ABSTRACT 1 polar solvent, in proportions of 15 to 50, referred to the copolymer.

9 Claims, No Drawings PROCESS FOR MAKING BRIGHTYARNS' The present invention relates to a process for making bright yarns which are homogeneous and stable at high temperature by spinning a copolymer containing amide-imide linkages and imide linkages and to the filaments and fibers thus obtained.

A process is disclosed in US. Pat. No. 3,415,782 for making bright filaments having a base of polypyromellitiimide of good longitudinal and transverse strength by the dry-spinning of a solution of a polyamide-acid obtained from pyromellitic dianhydride and bis(amino- 4-phenyl) ether or bis (amino-4-phenyl) sulfide and then transforming the polyamide-acid into polyimide by subsequently heating the resulting filaments. However, such a process has the disadvantage of being rather complicated technically because dry-spinning requires extensive apparatus and high evaporation-cell temperatures.

It is also known, from French Pat. No. 1,566,393, to prepare films by casting copolymers in solution obtained from a prepolymer containing amide and imide groups and a prepolymer containing imide groups and then heating to evaporate the solvent. However, the inherent viscosities of these copolymers are low and generally less than 0.5, which does not make it possible to obtain yarns of good quality. I

The polyamide-imide yarns prepared by heretofore .available wet-spinning processes are heterogeneous,

lusterless and porous and therefore unsuitable for any textile use.

It has also been proposed to introduce linkages bearing alkaline sulfonate groups into polyamide-imide polymers to be spuninto fibers but the presence of an alkaline metal is not always desirable.

it is therefore an object of this invention to provide a method for making bright yarns from polymers which contain both amide-imide linkages and imide linkages.

Another object of the invention is to provide an imacid groups in a polar organic solvent therefor into a solvent-non-solvent coagulating bath. The unreacted carboxyl groups in the copolymer should be equivalent to at least 0.5 acid milliequivalent per gram of dry copolymer. The inherent viscosity of the copolymer should be between 0.7 and 1.5. The copolymer may be prepared by reacting at a temperature of less than 80C in a polar organic solvent, a polyamide-imide and a polyamide-acid containing reactive isocyanate' groups. Preferably, the copolymer contains to 50% polyamide acid. The spun copolymer after coagulation is drawn in air at room temperature, washed and dried by conventional methods and overdrawn at an elevated temperature. The dried product may be heat treated by a conventional method, if desired, before overdrawing. A solution of copolymer having an inherent viscosity of between 0.7 and 1.5 which is suitable for wetspinning may be prepared in accordance with this invention by mixing a solution of polyamide-imide with a separately prepared fresh solution of polyamide-acid prepolymer but it is preferably prepared by forming the 5 polyamide acid in situ in a solution of previously prepared polyamide-imide. The high viscosity of the copolymer tends to establish that a branched and/or sequential copolymer is obtained.

The polyamide-imide may be prepared by reaction in substantially stoichiometrieal proportions in anhydrous polar organic solvent of at least one aromatic diisocyanate with an acid reagent formed of an aromatic acid anhydride and possibly a small proportion of an aromatic diacid, for example, up to terephthalic acid or the like. The polyamide-imide obtained has the following amide-imide linkages:

and possibly amide linkages of the formula:

-NHAr,NHCORCO in which R represents an aromatic divalent radical, Ar, represents a divalent aromatic radical, and Ar represents a trivalent aromatic radical having at least 6 carbon atoms.

Any suitable aromatic diisocyanate may be used. Preferred diisocyanates are 4,4'-diisocyanato-diphenyl methane, 4,4-diisocyanatodiphenyl ether, 4,4-

diisocyanato-diphenyl propane, 2,4-toluylene diisocyanate, meta phenylene diisocyanate, para phenylene diisocyanate, 1,5-naphtylene diisocyanate and the like.

- Suitable acid anhydrides include trimel'litic anhydride and among the suitable aromatic diacids, terephthalic acid isophthalic acid, 4,4'-dicarboxy diphenyl methane, 4,4'- dicarboxy diphenyl ether, 4,4- dicarboxy diphenyl sulfone, 4,4'-dicarboxy diphenyl benzophenone, 4,4'-dicarboxy diphenyle are particularly well suited.

The reaction takes place at a temperature which can range, for instance, from 80 up to 180C and even more. A preferred method of preparation consists in gradually raising the temperature of the reaction medium, for instance, for l to 3 hours and then maintaining this temperature for a period of time which may vary from 1 to 4 hours.

The reaction takes place in an anhydrous polar organic solvent, preferably N-methyl pyrrolidone, so as to obtain a polymer concentration in the solution of between 18 and 35% by weight, and preferably between 22 and 28%, without taking into consideration a possible dilution at the end of the operation. The inherent viscosity of the polyamide-imide obtained (measured in a 0.5% solution in N-methyl pyrrolidone at C) is generally between 0.5 and 1.2 and generally close to The polyamide-acid prepolymer is obtained by reaction, in substantially stoichiometric proportions in the same organic solvent, of an aromatic diisocyanate (preferably the same that used for preparing the polyamide-imide) with an acid reagent formed of a tetracarboxylic acid dianhydride alone or mixed with the corresponding tetracarboxylic acid in the presence of a small amount of water, which may range up to about 3% by weight, based on the weight of solvent.

The starting temperature is generally between about 25 and about 40C. It is preferably maintained within these limits for several hours. lt is possible then gradually to increase the temperature without, however, going beyond 80C, which would transform too many amide-acid groups into imide groups. The prepolymer then becomes insoluble. its concentration in the solution is generally between and 24%.

in the event that a previously prepared polyamideimide is used as is preferred it is obviously necessary to cool it to less than 80C and preferably to a temperature of between 25C and 40C before introducing the components of the polyamide-acid.

Among the tetracarboxylic acid dianhydrides mention may be made, for instance, of the pyromellitic and benzophenone3,4,3',4-tetracarboxylic dianhydrides. At the time that it is mixed with the polyamide-imide solution, the polyamide-acid solution must necessarily be freshly prepared (in the event that it is prepared separately) so that the polymer contains a maximum number of reactive isocyanate groups. In practice this solution must be used within 24 hours after its preparation.

The inherent viscosity of the polyamide-acid is generally of the order of about 0.4 to 0.5.

-This value is not sufficient to permit wet-spinning under good conditions.

Under the conditions of the invention, there is obtained a copolymer whose inherent viscosity is generally greater than the.inherent viscosity of the polyamide-imide and the polyamide-acid prepolymer used separately, which permits the wet-spinning of the solutions of the copolymer under good conditions.

The determination of the reactive isoeyanate groups of the polyamidc-acid leads to the assumption that a branched and/or sequential copolymer is formed by reaction of the isocyanate groups with mobile H functions of the polyamide-imide, since there is simultaneously noted an increase in the inherent viscosity of the copolymer obtained.

Moreover, the copolymer thus obtained has a content of free carboxyl groups greater than 0.5 (this content being expressed in milliequivalents per gram of dry copolymer). The best homogeneity and the best characteristics of the yarns are obtained with rates of free carboxyl groups at least equal to 0.6.

The proportions of polyamide-imide and polyamideacid in the copolymer wet-spun in accordance with the present invention are between 50 and 85% polyamideimide and 15 and 50% polyamidc-acid based on the I weight of copolymer. The preferred composition is 80% polyamide-imide and by weight polyamideacid.

The solvent may be any suitable polar organic solvent such as dimethyl acctamide, tctramethylene sulfone, or the like, preferably N-methyl pyrrolidone.

N-methyl pyrrolidone is poorly suited for the preparation of polyamide-acids of high molecular weight; on the other hand, it permits good reproducibility of the characteristics of the polyamide-imide and the polya mide-acid; surprisingly, copolymers of high molecular weight are obtained in this solvent. This is why N- methyl pyrrolidone constitutes the preferred solvent in the process claimed.

The spinning of the solution of the copolymer as described above is earried out in a coagulating bath composed essentially of solvent and non-solvent, generally at room temperature.

As non-solvent for the copolymer which can be used in the coagulating bath, mention may be made, for instance, of glycol, acetone, methylene chloride, although water is generally preferred for obvious reasons of economy.

The filaments are drawn, preferably in air, at a slow rate, and then washed, for instance on rollers, possibly with counter-current flow, and preferably with water, and dried, for instance on rollers, preferably at temperature of about to 300C. Thereupon the yarn is subjected to another drawing at elevated temperature, generally above 300C, and possibly up to 400C, and even beyond, by any means known to the man skilled in the art, for instance, in a tube or on a heating plate. Thus, in the copolymer, amid-acid groups are transformed into imid groups.

If it is desired to obtain filaments having particularly high mechanical properties, in particular excellent tenacity, one can effect a heat treatment before the last drawing, for instance at a temperature of between 200 and 300C.

The yarns obtained, in addition to their brightness, have excellent physical and mechanical properties, and in particular good thermal stability and good non-inflammability.

The textile applications of the yarns thus obtained are extremely varied protective clothing, equipment, conveyor belts, filtration of hot gases, etc.

The following examples in which the percentages are percentages by weight are given by way of illustration and not of limitation in order to illustrate the invention.

Example 1 There are prepared separately: A. On the one hand, a polyamide-imide solution from a mixture of:

4.4'-diisocyanato-diphcnyl methane 875 g trimellitic anhydridc 672 g N-methyl pyrrolidone 3349 g The polymer thus obtained has an inherent viscosity of 1.00 and has no free isocyanate groups.

B. On the other hand, a polyamide-acid solution from a mixture in stoichiometric proportions of:

4,4'-diisocyanato-diphcnyl methane 250 g pyromellitic dianhydride 2 l 8 g N-methyl pyrrolidonc containing 0.8% water 1730 g There is obtained a prepolymer of an inherent viscosity of 0.40, having a content of isocyanate groups of 1.83 (expressed in milliequivalents per gram of dry prepolymer) and a content of earboxylic groups of 3.77 (expressed in milliequivalents per gram of dry prepolymer).

The two solutions A and B are mixed in different proportions so as to obtain C, D, E, F, G containing l0, 15, 20, 35 and 50% respectively of polyamide-aeid prepolymer.

The determination of the isocyanate groups on the prepolymer and the copolymer is effected immediately after the reaction by potentiometry at room temperature in dimethyl aeetamide. After the determination on the copolymer there is noted the practically complete disappearance of the isocyanate groups (see Table l).

and 19.2% respectively; thereupon each of the solutions is spun separately through a spinneret of 64 holes of a diameter of 0.05 mm into a coagulating bath containing 60% N-methyl pyrrolidone and 4071 water, maintained at room temperature.

The filaments are then washed with water in countercurrent, at room temperature, and then dried on rollers at 80C and then at 170C, drawn at room temperature, at rates given in Table 1 below. They are then heat treated in an oven for 2 hours at 240C and drawn again at 420C in a tube at rates indicated in Table I below, which sets forth the characteristics of the polymers and of the yarns obtained.

lt is noted that the yarns obtained from copolymers D, E, F. G are bright, contrary to the yarn obtained from copolymer C the content of COOH groups of which is insufficient.

The heat stability of sample E was evaluated by the loss of strength upon aging. as follows:

for 300 hours at 177C: for 1000 hours at I77C:

Example 2 A polyamide-imide is prepared from:

diisocyanato-4.4'-diphenyl ether trimellitic anhydride N-methyl pyrrolidone 630 g 480 g 2818 g The polymer obtained has an inherent viscosity of 1.05.

There is introduced into the previously prepared polyamideimide solution. cooled to 38C:

diisocyanato-4A'-diphcnyl ether 32 g pyromellitie dianhydride 27.7 g N-methyl pyrrolidone 104 g water 1.37 g

During the course of 2 hours, 190 g of N-methyl pyrrolidone and 1.37 g of water are added at 38C, maintaining this temperature for 1 hour. whereupon the temperature is increased to about 60C, which temperature is maintained for another hour. Prepared separately. theprepolymer has an inherent viscosity of 0.53. The copolymer obtained, which has an inherent viscosity of 1.39 and a content of carboxylic acid groups of 0.78 is spun in solution in N-methyl pyrrolidone at a concentration of 23.1% through a spinneret of 64 orifices of a diameter of 0.05 mm into a coagulating bath composed of N-methyl pyrrolidone and water, in a proportion of 60:40. at room temperature.

The yarn obtained is washed with water on rollers at room temperature, and then dried on two drying rollers of a temperature of and C respectively.

After drawing in air at a rate of 1.22, the yarns undergo a second drawing in a tube at 400C, at a rate of 2.50.

The properties of the yarns are as follows:

Count 446 dtex Dry strength in g/tex 43 Elongation. dry 71 8.2 Aging:

after 300 hours at 177C +9.47: Loss of Strength after 1000 hours at 177C 34'/( v Appearance very bright.

Although the invention has been described in detail for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.

We claim: 1

l. A method for making a non-inflammable heatstable, bright yarn comprising 1. wet-spinning into a coagulating bath a solution in g a polar organic solvent of a copolymer which contains both amide-imide groups and amide-acid 2. The method of claim 1 wherein the copolymer contains from 15 to 50% polyamide-acid.

3. The method of claim 1 wherein the washed and dried filaments are heat treated; prior to overdrawing.

4. The method of claim 1 wherein the solvent in the spinning solution and the coagulating bath is N-methyl pyrrolidone.

5. The method of claim 1 wherein the polyamide-acid is prepared in a solution containing the polyamideimide solution.

6. The method of claim. 1 wherein the polyamideimide is the reaction product of? an aromatic diisocyanate and trimellitie anhydride and the polyamide-acid is the reaction product of an aro matie diisocyanate and pyromellitic dianhydride.

7. The method of claim 5 wherein the diisocyanatc used in each reaction is 4.4'-diphenylmethane diisocyanate.

8. The method of claim 1' wherein an aromatic dicarboxylic acid is included in the preparation of the polyamideimide.

9. A non-inflammable, heat-stable, bright yarn pre- 

1. A METHOD FOR MAKING A NON-INFLAMMABLE HEAT-STABLE BRIGHT YARN COMPRISING
 1. WET-SPINNING INTO A COAGULATING BATH A SOLUTION IN A POLAR ORGANIC SOLVENT OF A COPOLYMER WHICH CONTAINS BOTH AMIDE-IMIDE GROUPS AND AMIDE-ACID GROUPS, THE FREE CARBOXYL GROUP CONTENT OF THE COPOLYMER BEING AT LEAST EQUAL TO 0.5 MILLIEQUIVALENTS OF ACID PER GRAM OF DRY COPOLYMER, SAID COPOLYMER HAVING AN INHERET VISCOSITY OF BETWEEN 0.7 AND 1.5, SAID COPOLYMER HAVING BEEN PREPARED BY REACTING IN A POLAR ORGANIC SOLVENT AT A TEMPERATURE BELOW 80*C A POLYAMIDE-IMIDE AND A POLYAMIDEACID PREPOLYMER,
 2. DRAWING THE RESULTING FILAMENTS IN AIR AT AMBIENT TEMPERATURE,
 2. drawing the resulting filaments in air at ambient temperature;
 2. The method of claim 1 wherein the copolymer contains from 15 to 50% polyamide-acid.
 3. The method of claim 1 wherein the washed and dried filaments are heat treated prior to overdrawing.
 3. washing and drying; and
 3. WADHING AND DRYING, AND
 4. OVERDRAWING THE PRODUCT AT AN ELEVATED TEMPERATURE.
 4. overdrawing the product at an elevated temperature.
 4. The method Of claim 1 wherein the solvent in the spinning solution and the coagulating bath is N-methyl pyrrolidone.
 5. The method of claim 1 wherein the polyamide-acid is prepared in a solution containing the polyamide-imide solution.
 6. The method of claim 1 wherein the polyamide-imide is the reaction product of an aromatic diisocyanate and trimellitic anhydride and the polyamide-acid is the reaction product of an aromatic diisocyanate and pyromellitic dianhydride.
 7. The method of claim 5 wherein the diisocyanate used in each reaction is 4,4''-diphenylmethane diisocyanate.
 8. The method of claim 1 wherein an aromatic dicarboxylic acid is included in the preparation of the polyamideimide.
 9. A non-inflammable, heat-stable, bright yarn prepared by the method of claim 1 from a copolymer which contains both amide-imide groups and amide-acid groups, said copolymer having a free carboxylic group content which is at least equal to 0.5 milliequivalents of acid per gram of dry copolymer and having an inherent viscosity of between 0.7 and
 15. 